Traditional microscopic inspection ring illuminators have either incandescent, fiber-optic or fluorescent light sources. Each of these traditional light sources exhibit problems which may contribute to decreased sample resolution and/or operator fatigue. The light output of incandescent bulbs decreases with distance from the bulb filament, rather than from the bulb surface as with fluorescent bulbs. As a result, the light incident on an object being inspected may be inconsistent, creating shadows and poor viewing. In addition, ring-shaped incandescent bulbs are extremely difficult to make. On the other hand, fiber-optic ring illuminators generally supply light all around an object being illuminated but have a relatively high cost and a relatively short life.
In contrast, fluorescent ring illuminators supply a relatively steady light output which can be directed almost all around an object being viewed. In addition, those light sources are relatively inexpensive and have a relatively long life. Therefore, fluorescent sources are best suited for microscopic inspection ring illuminators.
Traditional fluorescent ring illuminators used as light sources for microscopic inspection typically lack many features which could contribute to superior illumination and decreased operator eye strain. These illuminators typically operate at 60 Hz. This relatively low frequency causes both flicker and hum, which contribute to user fatigue and may decrease productivity of an operator using an inspection device with this conventional light source. In addition, the 60 Hz frequency interferes with high resolution image processing because most image processing equipment in the United States operates at a vertical scan rate of 60 Hz. Thus, a traditional fluorescent light source used in conjunction with this image processing equipment may cause generation of dark interference bands on a video output screen as a result of the coincidence of light flicker frequency and video scan rate.
As these fluorescent ring illuminators are traditionally used as microscope mounted light sources, it would be desirable to have the capability of dimming and brightening the light source to illuminate different objects for visual inspection. Presently, fluorescent illuminators do not have dimming and brightening capabilities. As a result, highly polished objects may appear very bright, and dull objects may appear too dark. These problems can also lead to increased eye strain and decreased productivity.
As with any electrical instrument, fluorescent illuminators should be properly grounded and shielded. Traditionally, the lamp housings for ring illuminators are non-metallic. Because of this, the housing cannot be grounded and does not protect the bulb from breaking. Also, the power feed cable of these illuminators is typically not shielded. This lack of shielding can cause video image problems if the illuminator is used in conjunction with image processing equipment, and/or the illuminator may interfere with operation of electrical devices in close proximity to it.